The present invention relates to a magnetic head device for recording electric signals on a magnetic tape as magnetic signals and converting magnetic signals, which have already been recorded on the magnetic tape, to electric signals for reproduction, and more particularly, it relates to a magnetic head device suitable for use in the magnetic recording/reproducing apparatus of the pulse-code modulation type.
The demand for a compact cassette-type recorder of the pulse-code modulation (which will be hereinafter referred to as PCM) type has rapidly risen recently. In the case of this PCM type compact cassette-type recorder, the number of tracks on the magnetic tape must be increased to about 18 to 36 to raise the magnetic recording density per a predetermined length of the magnetic tape in a compact cassette. When the number of tracks is increased like this, however, the width of one track will become 100 to 200 .mu.m. Therefore, the real width for recording will become narrower, ranging from 50 .mu.m to 100 .mu.m, since it is obtained by subtracting the guard band from the width of one track.
In the case where magnetic signals, recorded on an actual recording track which ranges from about 50 .mu.m to 100 .mu.m, are converted to electric signals for reproduction by means of the magnetic reproducing head in the compact cassette-tape recorder, tracking error of the actual recording track on the magnetic tape, relative to the gap of the magnetic reproducing head, must be held to an extremely small range, for example, a maximum of less than 20 .mu.m.
The following two measures are supposedly used for reducing the tracking error of a magnetic tape.
The first uses a tape guide of the conventional type to track the magnetic tape, relative to the gap of the magnetic reproducing head. Since the tracking error allowed in this case is extremely small, ranging 20 .mu.m at maximum, and manufacture and assembly of the tape guide must be done with extremely high accuracy, the manufacturing cost of the compact cassette-tape recorder is extremely high. In addition, the magnetic tape is forcibly tracked by the tape guide and thus likely to be damaged by its sliding contact with the tape guide. Further, a fatal drawback, caused when employing the first measure, is that the tracking adjustment of the tape guide is almost meaningless, even if the tracking of the magnetic tape can achieve a high level of accuracy the point of view of manufacture and assembly of the tape guide, because the width of a magnetic tape in the commercially-available compact cassette is determined to range from 3.81 mm to 3.76 mm, according to the standard and manufacturing maximum tolerance of 50 .mu.m allowed in the width of the magnetic tape itself.
In contrast, the second measure causes the magnetic reproducing head to follow an actual recording track of the magnetic tape. An example of using this second measure is the well-known head moving device disclosed in Japanese Patent Disclosure No. 56-74822. The well-known head moving device comprises a base, a pair of parallel leaf springs whose proximal ends are fixed to the base, a magnetic recording/reproducing head attached to the distal ends of these parallel leaf springs, and displacing means for displacing the paired parallel leaf springs which oscillatingly move the magnetic recording/reproducing head to follow the magnetic tape or the waving of its actual recording track.
In the case of the above-described head moving device, the parallel leaf springs extend perpendiclar to the direction in which the magnetic tape runs, and contact pressure, which is added to the head surface of the magnetic recording/reproducing head because of tension of the magnetic tape and pad pressure is therefore transmitted to the parallel leaf springs through the magnetic recording/reproducing head. In short, the contact pressure acts as compression force on the parallel leaf springs from the distal ends to the proximal ends thereof. When the parallel leaf springs are displaced so as to follow the waving of the magnetic tape, buckling of the parallel leaf springs is thus likely to be caused by the compression force. Therefore even if the displacement of the parallel leaf springs is controlled by the displacing means to follow a shift which corresponds to the waving of the actual recording track on the magnetic tape so as to achieve the tracking of the magnetic recording/reproducing head, the head will fail to achieve the high accurate tracking due to the fact that the buckling of the parallel leaf springs may occur by the compression force. This means that displacing force, added to the parallel plate springs from the displacing means, is not linearly proportional to the displacement of the parallel plate springs caused by the displacing force.
In order to prevent the buckling of the parallel leaf springs, it is supposed that the thickness of each of the parallel leaf springs is increased and that the stiffness of the parallel leaf springs is thus risen. If so made, however, a large and strong displacing means is needed to displace the parallel leaf springs, thus increasing the cost of the magnetic head device and increasing the weight of the whole magnetic head device due to increase the weight of the parallel leaf springs and displacing means. In other words, when stiffness relative to the displacement of the parallel leaf springs is determined, stiffness relative to the compression force is also determined unconditionally, thus making it impossible to freely design the magnetic head device.
Further, the magnetic recording/reproducing head and the parallel leaf springs are connected to each other in a series in the head moving device, thus making the whole of the head moving device large.